.TH std::uninitialized_fill_n 3 "2024.06.10" "http://cppreference.com" "C++ Standard Libary"
.SH NAME
std::uninitialized_fill_n \- std::uninitialized_fill_n

.SH Synopsis
   Defined in header <memory>
   template< class ForwardIt, class Size, class T >
   ForwardIt uninitialized_fill_n( ForwardIt first, Size count, const \fB(1)\fP
   T& value );
   template< class ExecutionPolicy, class ForwardIt, class Size,
   class T >

   ForwardIt uninitialized_fill_n( ExecutionPolicy&& policy,          \fB(2)\fP \fI(since C++17)\fP

                                   ForwardIt first, Size count, const
   T& value );

   1) Copies the given value value to the first count elements in an uninitialized
   memory area beginning at first as if by for (; n--; ++first)
       ::new (/* VOIDIFY */(*first))
           typename std::iterator_traits<ForwardIt>::value_type(value);
   where /* VOIDIFY */(e) is:

   static_cast<void*>(&e)                \fI(until C++11)\fP
   static_cast<void*>(std::addressof(e)) \fI(since C++11)\fP

   If an exception is thrown during the initialization, the objects already constructed
   are destroyed in an unspecified order.
   2) Same as \fB(1)\fP, but executed according to policy. This overload participates in
   overload resolution only if

   std::is_execution_policy_v<std::decay_t<ExecutionPolicy>> is true.        (until
                                                                             C++20)
   std::is_execution_policy_v<std::remove_cvref_t<ExecutionPolicy>> is true. (since
                                                                             C++20)

.SH Parameters

   first            -           the beginning of the range of the elements to
                                initialize
   count            -           number of elements to construct
   value            -           the value to construct the elements with
.SH Type requirements
   -
   ForwardIt must meet the requirements of LegacyForwardIterator.
   -
   No increment, assignment, comparison, or indirection through valid instances of
   ForwardIt may throw exceptions.
   Applying &* to a ForwardIt value must yield a pointer to its value type.
   \fI(until C++11)\fP

.SH Return value

   Iterator to the element past the last element copied.

.SH Complexity

   Linear in count.

.SH Exceptions

   The overload with a template parameter named ExecutionPolicy reports errors as
   follows:

     * If execution of a function invoked as part of the algorithm throws an exception
       and ExecutionPolicy is one of the standard policies, std::terminate is called.
       For any other ExecutionPolicy, the behavior is implementation-defined.
     * If the algorithm fails to allocate memory, std::bad_alloc is thrown.

.SH Possible implementation

   template<class ForwardIt, class Size, class T>
   ForwardIt uninitialized_fill_n(ForwardIt first, Size count, const T& value)
   {
       using V = typename std::iterator_traits<ForwardIt>::value_type;
       ForwardIt current = first;
       try
       {
           for (; count > 0; ++current, (void) --count)
               ::new (static_cast<void*>(std::addressof(*current))) V(value);
           return current;
       }
       catch (...)
       {
           for (; first != current; ++first)
               first->~V();
           throw;
       }
   }

.SH Example


// Run this code

 #include <algorithm>
 #include <iostream>
 #include <memory>
 #include <string>
 #include <tuple>

 int main()
 {
     std::string* p;
     std::size_t sz;
     std::tie(p, sz) = std::get_temporary_buffer<std::string>(4);
     std::uninitialized_fill_n(p, sz, "Example");

     for (std::string* i = p; i != p + sz; ++i)
     {
         std::cout << *i << '\\n';
         i->~basic_string<char>();
     }
     std::return_temporary_buffer(p);
 }

.SH Output:

.SH Example
.SH Example
.SH Example
.SH Example

   Defect reports

   The following behavior-changing defect reports were applied retroactively to
   previously published C++ standards.

      DR    Applied to          Behavior as published              Correct behavior
                       given T as the value type of ForwardIt,
   LWG 866  C++98      if                                      uses global replacement-
                       T::operator new exists, the program     new instead
                       might be ill-formed
                       the location of the first element
   LWG 1339 C++98      following                               returned
                       the filling range was not returned
   LWG 2433 C++11      this algorithm might be hijacked by     uses std::addressof
                       overloaded operator&
   LWG 3870 C++20      this algorithm might create objects on  kept disallowed
                       a const storage

.SH See also

                                copies an object to an uninitialized area of memory,
   uninitialized_fill           defined by a range
                                \fI(function template)\fP
   ranges::uninitialized_fill_n copies an object to an uninitialized area of memory,
   (C++20)                      defined by a start and a count
                                (niebloid)
